1. Field of the Invention
The present invention relates to methods for concentrating and/or purifying a fat-soluble trace constituent contained in a plant. The present invention also relates to methods for making a concentrated and/or purified fat-soluble trace constituent of a plant and the concentrated and/or purified fat-soluble trace constituent of a plant prepared by such a method. The present invention further relates to food products that include such a concentrated and/or purified fat-soluble trace constituent and methods for making such a food product.
2. Discussion of the Background
Plant tissues contain fat-soluble trace constituents having useful physiological activating functions, such as plant sterols and tocopherols. In order to concentrate such trace constituents, a method where by-products and scum produced in a deodorizing process for edible plant oil are subjected to molecular distillation or the like has been commonly carried out. A method is known where, at that time, a fatty acid having 10 to 22 carbons is added to a distillate of the plant oil so as to esterify sterol, etc., and then a molecular distillation is carried out to concentrate the aimed constituents (see, Japanese Patent Laid Open No. 10-508605).
On the other hand, particularly with regard to spices and flavors, the following method has come into wide use: a medium-chain fatty acid triglyceride (MCT) is used as an extracting solvent whereby the desired trace constituents are concentrated.
For example, the following methods have been known: a method where MCT is added to a fermented food, extraction by heating and filtration is conducted, and a highly oil-absorbing dextrin is added to the liquid extract, to yield an edible flavor preparation (see, Japanese Patent Laid Open No. 05-003764); and a method where roasted sesame oil is subjected to steam distillation and MCT is added to the resulting distillate to obtain a roasted sesame flavor (see, Japanese Patent Laid Open No. 2001-112432).
However, when the aforementioned trace constituents are solid or a viscous liquid at ordinary temperature (25° C.) and, further, they are present in very low concentrations in a raw material, there is a problem that, when a mere molecular distillation is conducted, they are firmly adhered onto a condensing surface so that a sufficient recovery rate is not achieved. Another disadvantage is that, even when an extracting operation is conducted using MCT as a solvent, the desired concentration of an aimed substance is not reliably achieved.
In view of the foregoing, there remains a need for a method of concentrating and/or purifying specific fat-soluble trace constituents that are hard to process, in which fixation of these trace constituents onto a condensing surface while conducting molecular distillation is prevented, such that a high quality concentration of these trace constituents is obtained.